Water remediation

ABSTRACT

A portable modular water air stripper system for remediation of contaminated water, such as groundwater at an outdoor contamination site, has its primary components, including the frames of a vertical assembly of individually demountable tray units, a sump and cap member, formed as hollow rotationally molded plastic pieces. Each tray unit has an air-porous sheet member having air-flow apertures with a diameter of 0.100 inches or less constructed to retain water during stripping action by air passing upwardly through the apertures. Each sheet member is removable from a respective tray frame and has mounted thereon a baffle that defines a tortuous water flow path across each tray. In one embodiment, the baffles extend between and are substantially sealed to the undersurface of the next higher tray. According to another feature, a transfer duct is arranged to guide the least contaminated groundwater downwards and laterally to a position in the next lowest tray unit whereby the water will contact the most contaminated air of the next lowest tray unit. In a further embodiment, a vacuum pump for drawing stripping air through the system is mounted on the sump within a protective enclosure which also covers an air inlet provided in the sump through which stripping air is drawn.

This application is a continuation-in-pan of U.S. application Ser. No.07/661,403, filed Feb. 26, 1991, now abandoned.

FIELD OF THE INVENTION

This invention relates to water remediation. More particularly, theinvention relates to a portable, modular stripping system usable totreat contaminate water on site, and an associated method of use.

BACKGROUND OF THE INVENTION

Remediation of contaminated water, such as hydrocarbon-contaminatedgroundwater which is the subject of an environmental clean-up project,can be achieved with an air stripper system, including a verticalstripping tower, installed temporarily at the site. The contaminatedwater is introduced to the top of the tower and caused to flowdownwardly by force of gravity, while stripper air is introduced fromthe bottom of the tower and caused to flow upward. The mixing of waterand air that occurs during this countercurrent flow results in thetransfer of the contaminants from the water to the airstream. Relativelyclean water collects at the bottom of the tower which can be re-used,e.g., re-introduced to the ground. The contaminated airstream exits thetop of the tower and is typically treated to remove the contaminantsprior to emission of the air to the atmosphere. The degree to which thecontaminants are removed from the water is dependent upon tactors suchas the height of the stripper tower and the volume of stripper airpassed through the tower. In general, an increase in decontaminationeffectiveness is achieved by increasing tower height and air flowvolume. The economics of such remediation and the difficulties ofmaintenance of units at remote locations are of important concern, asare esthetics in many instances.

SUMMARY OF THE INVENTION

The invention provides a low physical profile remediation system havinga compact, modular air stripping unit that enables easy servicing andlow-cost operation, and which is aesthetically more pleasing than hightowers. One aspect of the invention comprises a water air strippersystem usable to treat contaminated water such as at an outdoor site inresidential areas near filling stations. the air stripper system usablewith a blower arranged to cause air flow upwardly through the stripperunit, the water air stripper system comprising a vertical assembly oflimited vertical height of a series of individually demountable trayunits mounted above one another, the bottom of each tray unit comprisedof air-porous medium defined by a sheet member having air-flowapertures, the apertures having a diameter of about 0.100 inch or lessto prevent the flow of water therethrough at zero or minimal airflowthrough the apertures under conditions of equality between the head ofwater in the tray above the aperture and the opposing pressuredifferential of the air below and above the respective tray, each trayconstructed to retain water for a period of time during stripping actioncaused by air passing upwardly through the apertures, water entry meansand exit means respectively at the top and bottom of the water airstripper system, and water-flow guiding means to guide the water at arelatively shallow depth over each stage of air-porous media, thencedownwards to the next stage; and air inlet and outlet conduitsrespectively at the bottom and top of the unit.

Another aspect of the invention comprises a water air stripper unitusable to treat contaminated water at a remediation site, the stripperunit comprising a vertically-extending interfitting nest of demountabletray frames, each tray frame having a porous bottom member which isremovable from the frame and an internal baffle that defines a tortuouswater flow path laterally across the bottom member of each tray, thebaffles extending respectively between and substantially sealed to, theundersurface of the next above tray bottom member and the upper surfaceof the tray bottom member in which the baffle resides.

Another aspect of the invention comprises a water air stripping unitusable to treat contaminated water at a remediation site, the stripperunit comprising a vertical assembly of limited vertical height of aseries of individually demountable tray units, and a transfer ductextending from each of most of the tray units downwards, the transferduct arranged to guide the least contaminated groundwater in itsrespective tray unit to flow downwards and laterally to a position inthe next lowest tray unit whereby the water will contact the mostcontaminated air of the next lowest tray unit.

The water-flow guiding means may comprise a transfer duct arranged toguide the least contaminated groundwater of a said tray unit to flowdownwards to a position in the next lowest tray unit such that the waterentering the next lowest tray unit will contact the most contaminatedair passing through said next lowest tray unit, preferably,substantially all the tray units being provided with such a transferduct, so aged. Each transfer duct may include a check valve to preventair flow therethrough during start-up. Baffle means may be sealed to thetop and bottom surfaces of successive tray bottoms in a manner toisolate airstreams passing through regions of water in a tray unit thathave different levels of contaminants. The baffle means defines a pathfor the flow of water laterally in the tray unit, the path determiningthe residence time in the unit of water entering the unit, in a flow ofcontinually decreasing contamination from the point of entry to thepoint of exit of the unit.

The patterns of the baffle means of the successive units may bepositioned substantially identically above one another, with the waterguided from tray unit to unit such that the water proceeds progressivelyin repeated fashion through the same pattern of airstreams as itprogressively releases its contaminants during its course of lateraltravel through each of the series of units. The vertically arrangedseries of baffle means may provide adjacent vertical columns for theflow of stripper air, the columns arranged to maintain, throughout theseries of tray units, at any lateral position in the water flow path, asubstantially consistent ratio of contamination concentration of the airand the water through which it passes.

An air stripper unit with some or all of the above features may bearranged in combination with a volatilized contaminant removal deviceconnected to receive contaminated air from the air stripper unit and anair blower arranged to cause air flow upwardly from the stripper unit,the volatilized contaminant removal unit constructed and arranged toremove volatilized water contaminants stripped from the water andcarried by the air as it moves through the water stripping unit,preferably the volatilized contaminant removal device comprises apreheater and an oxidation unit or an absorbent or adsorbent.

Also, a preferred embodiment of the system is constructed todecontaminate water at a flow rate of about 20 gpm; the system isconstructed for an air flow rate of about 250 CFM or less; the air isdrawn into the stripper unit from a blower or vacuum pump, the intake ofwhich is connected to the top of the stripper unit; the air flow volumeof the stripper air is variable over a range of about 20 to 1; the airporous medium is removable and disposable; the air-porous medium hasopenings of about 0.050 inch; the air porous medium is a thin, flexiblesheet of thickness 0.06 inch or less; the air-porous medium has an openarea in the range of 2 to 9%, most preferably about 4 or 5%; theassembly of tray units may be arranged such that the size of theopenings decreases in successive tray units from the top of the stripperunit; the stripper tray units have an area of less than about 1000 in² ;the tray units have peripheral frames formed of rotationally moldedplastic; the sump is formed of rotationally molded plastic; and thestripper tray units have a vertical height of about six inches; the airstripper comprises at least five of said tray units, most preferably sixto ten of the tray units; and the stripper has a vertical height ofabout nine feet or less.

Another aspect of the invention comprises a method of treatingcontaminated water having the following steps. Contaminated water ispumped to an elevated position. The water is directed to flow laterallyacross and downwardly through a series of substantially horizontal trayssealed to each other to form a stripping apparatus. Air is drawnupwardly through the stripping apparatus, while the water flowsdownwardly from tray to tray through downcomers and laterally across aperforated area of the trays, in such a manner that the air passesthrough apertures of the perforated area having a diameter of about0.100 inch or less and through the water as it flows laterally acrosseach tray, whereby contaminants in the water are transferred to the airflowing upwardly with substantially no water seepage through theapertures. Air is exhausted from the stripping apparatus for subsequenttreatment. Finally, decontaminated water which is passed through thestripping apparatus is directed to flow to a predetermined storagelocation.

In another aspect, the invention resides in a portable modular strippersystem usable to treat contaminated water on site. The stripper systemhas a plurality of individually demountable and interchangeable trayunits stacked one on top of another to form a stripping column. Eachtray unit comprises a hollow plastic molded tray frame, a sheet memberhaving air-flow apertures, a baffle defining a lateral water flow pathacross each sheet member, a transfer duct or downcomer arranged to guidewater through the sheet member after having traversed the lateral waterflow path, and sealing means for creating an air and water tight sealbetween adjacent tray frames when the tray units are stacked to form thestripping unit. Water entry and exit means are provided at upper andlower ends of the stripping unit, respectively, for providing water flowthrough the stripping unit. Air entry and exit means are provided at thelower and upper ends, respectively, for providing an air flow throughthe water flowing in the stripping unit.

Another aspect of the invention comprises a liquid remediation apparatusfor stripping contaminants from a liquid via air flow. The apparatuscomprises a plurality of individually demountable tray units stackablevertically one on top of another to form a stripping column. Each trayunit comprises a sheet member having air-flow apertures (a perforatedarea), and a baffle defining a lateral water flow path across the sheetmember of each tray unit. The lowermost tray unit may be sealablysecured to a sump for storing decontaminated water passed through thestripper unit. A vacuum pump is mounted on the sump for drawing airthrough the stripper unit. Finally, enclosure means are mounted on thesump for enclosing the vacuum pump and coveting an air inlet in the sumpfor drawing air from within the enclosure means through the strippingunit. The enclosure means has a first passageway for allowing air toenter the enclosure means and a second passageway for exhausting airfrom the vacuum pump. The air drawn into the stripper unit initiallypasses over and cools the vacuum pump within the enclosure means.

The air stripper unit and method of the invention enhance the exposureof contaminated water to stripping air and increase efficiency of masstransfer from the water to the stripping air. Such operation enables theamount of stripping air to be kept in the same general range as occurswith tall counterflow packed towers, thus permitting low costdecontamination of the air before exhausting to the atmosphere. Ingeneral, the system, employing an air porous medium that does not relyon air flow to prevent the leakage of water downward through the bottomsof the tray unit, enables a wide range of ability to vary air flow andselection of a smaller and more economical unit for removal ofvolatilized contaminants from the stripper airstream. The air-porousmedium is preferably an aperture plate. The apertures are sized suchthat under a stable condition, in which the pressure differential of thestatic air below the aperture and above the water in the stageapproaches the pressure of the water column over the aperture, thesurface tension of the water prevents leakage of water through theapertures, even when substantially no air is passing through the holes.To meet this design parameter the apertures are sized at a maximum ofabout 0.100 inch, preferably, about 0.050 inch. At aperture sizes largerthan this, a substantial flow of air is generally required to minimizeleakage through the aperture. Thus, the present invention enablesvarying the air flow over a wide range and enabling the air flow to belimited to the minimum required to achieve the desired waterdecontamination. Thus the invention allows using a lower flow ratecapacity and therefore lower cost air decontamination system. In typicalsystems according to the invention, the air flow may be controlled overa range of 20 to 1. In some practical embodiments, because of the largepressure drop employed in the stripper unit, a relatively large highenergy blower may be required. The air flow rate required, as discussedabove, may be comparatively low, e.g., 100 cfm, enabling the use of arelatively small air decontamination unit. Where an oxidation unit isemployed, the consumption of input energy in heating the air forcombustion can be minimized. The overall energy consumption of thesystem therefore can be kept comparatively low. The cost of systemmaintenance likewise is greatly reduced by the low physical profile andthe novel construction features of the invention.

The hollow rotationally molded plastic construction of the trays, capmember and sump of both the first and second illustrated embodimentsprovide a highly durable yet lightweight modular unit particularlysuitable for easy setup and operation at remote sites. Assembly of thesystem is greatly facilitated by the fact that the tray frames areidentical and completely interchangeable.

The system configuration can be varied to tailor operation to therequirements of a particular outdoor site, to provide a small (generallyless than 8 or 9 feet tall), easily portable, adaptable decontaminationsystem that satisfies the myriad of varying performance, maintenance,power and aesthetic requirements of decontamination of outdoor sites,which can vary both from site to site and at any particular site, overtime. The modular construction of the stripper unit, and low physicalprofile provides for easy and economical replacement of the air-porousmedium to allow selection of aperture size and percent open area, thus,tailoring the air flow to the specific conditions encountered i.e.,actual on-site conditions of water flow, which may differ from estimatesmade before the system is installed. In addition, if higher percentageremoval is required, more stages over a wide range of smaller incrementscan be employed. During use, if fouling of the air-porous medium occurs,the medium can be easily replaced or cleaned (e.g.. by flexing orwashing the medium) by disassembly of the stage units. Furthermore, thenovel construction enables complete maintenance to be performed atremote sites by a small crew, which may be only one man.

In the embodiment of FIGS. 6-10, since the vacuum pump is mounted to thesump and surrounded by an enclosure, transportation of the entireapparatus as a single unit is facilitated, and the advantage of vacuumpump cooling is obtained by drawing air through the pump enclosure.Also, the simplified baffle and transfer duct arrangement of the secondembodiment has reduced manufacturing and maintenance costs as comparedwith the fast, while still obtaining excellent decontaminationefficiencies.

Other features and advantages of the invention will be apparent andfully understood from the following detailed description of thepreferred embodiments, taken in connection with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first remediation system in use totreat contaminated water at an outdoor site; while FIG. 1a is a sideview of the stripper unit.

FIG. 2 is a cross-sectional view of a low physical profile air stripperunit, indicating the vertical flow of water and air; FIG. 2a is across-sectional view along the lines a--a in FIG. 2, illustrating thelateral flow of water; FIG. 2b illustrates an air permeable medium thatprevents the flow of water therethrough at zero air flow.

FIG. 3 is a plot of the relative contaminant removal efficiency versusvertical stage for a water stream under treatment; FIG. 3a is a plot ofrelative logarithmic contaminant concentration of water and air as afunction of lateral position in a treatment tray;

FIG. 4 is an exploded view of a tray unit employed in the stripper ofFIG. 2; FIG. 4a is an enlarged view of an air-porous medium; FIG. 4b isa cross-sectional view of a transfer duct, enabling water flow from onetray unit to its adjacent unit below; FIG. 4c illustrates a sealingmember employed with the tray units.

FIG. 5 illustrates the coupling of adjacent tray units; FIG. 5a is anenlarged view of the gasket seals in circle A of FIG. 5; FIG. 5b is anenlarged view of a single seal, shown in FIG. 5.

FIG. 6 is a side-view, partially in cross-section, of a low physicalprofile air stripper system in accordance with an alternative embodimentof the invention.

FIG. 7 is a frontal view of the stripper system illustrated in FIG. 6.

FIG. 8 is an exploded view of the tray unit employed in the strippersystem of FIGS. 6 and 7; FIG. 8a is a partial exploded view showing analternative preferred design for a water transfer duct.

FIG. 9 is a cross-sectional view illustrating two of the tray unitsshown in FIG. 8 assembled and coupled together.

FIGS. 10a and 10b are plan views of adjacent tray units which would beplaced one above the other, illustrating the opposite flow paths ofwater across adjacent trays.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Structure andOperation

Referring to FIG. 1, there is shown a low physical profile remediationsystem 2 at an outdoor site where groundwater 4 has been contaminatedwith organic contaminants 6 seeping from a storage tank 8 (which may beabove ground, as shown, or below ground) through strata 10. The system 2includes a pump 12 (e.g., 1 HP) immersed within the aquifer 4 to createa cone of depression 13 in the aquifer by rapid withdrawal of water(e.g., 20 gallons/minute) such that spread of the contaminant 6 iscontrolled and contaminant concentration is maximized in the area of thepump from which water is drawn for treatment. The contaminated water ispassed through pipe conduits 14 (e.g., 1.5 inch diameter) to an inlet 15near the top of a vertical, low physical provide air stripper apparatus16. The air stripper apparatus includes a stripper base 66 with an airinlet 18 through which air is drawn (e.g., 250 cfm or less--"cfm" as itappears throughout this application refers to standard cubic feet perminute) from the environment by virtue of pressure differential createdby a vacuum pump 20 (e.g., 3-5 HP), and creates a stripper airstreamwhich flows upwardly through a series of stripper trays 30-44 and incountercurrent flow to the contaminated water, simultaneously flowinglaterally and downwardly through the stripping apparatus by virtue ofgravity as will be further discussed. An advantage of the blower (vacuumpump) arrangement of this preferred embodiment is that air is pulledthrough the stripper rather than pushed through to create negativepressure within the system, thus inhibiting leakage of contaminated airout and thereby avoiding collection of contaminant gases, e.g., gasolinevapors, at sites where the apparatus is housed indoors or otherwiseconfined. Additionally, the negative pressure in the system has beenfound to increase the mass transfer of contaminant species, e.g.,volatile hydrocarbons, from the water to the air.

Referring as well to FIG. 2, substantially clean, contaminant-free water68 collects (via piping 70 that accesses the final tray 44) in a sump 23(e.g., rotationally molded polyethylene, 3/16 inch wall thickness) inthe base 66 at the bottom of the stripper, from which it is dischargedby gravity through pipe ducts 22 (e.g., 2 inch diameter) back into theaquifer by means of a recharge gallery 24 (length e.g., 15 feet) at apoint remote from depression 13. (A sump pump may be provided). The airexits the stripper 16 carrying high concentrations of contaminantsstripped from the water, passes through mist eliminator 60 (FIG. 2) incapping piece (cap member) 62 and through the outlet 17 to pipe ducts 26(e.g., 3 inch diameter). A pressure gauge 120 is provided to measure thepressure in the stripper. The contaminated air is introduced by blower20, whose intake is connected to the top of the stripper at 64 to an airdecontamination device 27 which may be, e.g., an oxidative unit or anadsorbent packing to remove the contaminants from the airstream prior toexhausting the air to the atmosphere through exhaust pipe 28. (In otherinstances it may be permissible to discharge the gaseous effluentdirectly to the atmosphere through an exhaust stack.)

The air decontamination device is preferably an oxidation unit ofrelatively small size (e.g., 8 by 5 by 7 feet high). Heated,VOC-carrying air flows upwardly from a preheater into a catalyticconverter containing a catalyst, e.g., a steel screen rolled into acylinder, coated with platinum, 3.25 inches high and 12 inches indiameter, as manufactured by Johnson-Matthey, through which contaminantcarrying air is caused to flow for conversion of the contaminantmolecules into carbon dioxide and water. The catalyst is encased ininsulation, e.g., Intrim® nonasbestos wrapping, manufactured by 3M ofMinneapolis, Minn., to contain the heat of reaction and to prevent thecontaminant carrying air from flowing around the catalyst. Optionally,the hot air, now essentially free of contaminants, flows through a ductinto a heat exchanger for transfer of heat from the hot, now clean airinto the contaminated air from the stripper stage. A suitable oxidationsystem is described in U.S. Pat. No. 4,892,664, assigned to the assigneeof the present application and hereby incorporated by reference.

The tray units axe constructed to be easily assembled and disassembledto tailor the stripping apparatus to the specific needs of the siteunder remediation and enable simple breakdown for transportation fromsite to site and ease of servicing on-site. The system can be assembledby a minimum number of workers. The small lightweight stages can becarried and assembled by a single worker. Each tray weighs, typically,about 30 lbs and has an area of less than 1000 in². The stripper traysare individually demountable by means of an interlocking mechanismincorporated in the tray frame 72 which firmly seals each tray to anadjacent tray (by means of seal members discussed further below). Thetrays are held together by means of two cloth straps 95, 96, the ends ofwhich extend from hooks 97 engaging eye bolts 98 on the base 66 (FIG.1a). The straps are released and tightened by a tie down ratchet 99. Thelow physical profile, i.e., height, enables the device to be easilyadapted for various water remediation requirements by the addition ofmore or fewer trays. In the embodiments particularly discussed herein,it has been found that two successive trays have a removal efficiency ofabout 90%. Typically, six to ten trays are employed. In an eight traysystem as illustrated, decontamination levels of 99.99% are achievable.Further, cleaning and replacement of e.g. the mist eliminator 60 or thetray bottoms 46 may be accomplished by workers laboring at relativelylow heights above the ground.

The low physical profile, typically a stripper tower height of abouteight or nine feet, overall, also satisfies aesthetic requirements ofoutdoor sites such as at filling stations located in residential areas.The entire remediation apparatus, including the stripper apparatus canbe conveniently housed in a room or hidden behind a single storybuilding. Referring to FIG. 2, in the embodiment shown, the overallheight of the stripper apparatus 16 is H₁, under 8.0 feet, the overallheight of the stages being H₂ about 4.5 feet, the height of the base 66being H₃ about 2.0 feet, the height of the capping piece 62, being H₄,about 0.5 feet and the height of each stage being H₅ about 0.5 feet.

Referring as well to FIG. 2a, the low profile stripper apparatus trayunits 30-44 are arranged to direct the flow of contaminated water andstripper air in a manner that optimizes efficiency of the strippingprocess by direction and control of water and air flow. Theeffectiveness of the stripper reduces requirements for air volume, thusreducing required pumping capacity of the air blower or vacuum pump 20and the decontamination capacity of the decontamination device 27, bothfactors contributing to the reduced physical profile and energyrequirements of the overall system. Each tray is separated from the trayimmediately below by an air-porous tray bottom member 46 which has aplurality of apertures 48 sized and configured such that water may beflowed thereover without seepage of the water through the apertures evenunder conditions of substantially zero air flow through the apertures.Preferably, the apertures are circular in shape and of a diameter ofless than 0.100 inch, most preferably about 0.050 inch and are spaced toprovide an open area of less than about 20%, typically, 2 or 3 to 8 or9%, and preferably 4 or 5%. The percent open area can be selected basedon the desired flow rate. Also, with smaller apertures, generallysmaller bubbles are formed in the water treated, enhancing surfacecontact and generally providing greater stripping efficiency. The traybottom is preferably formed of an economical, thin, flexible material,e.g. stainless steel, or suitable plastic that resists fouling and maybe disposed of after use.

Referring to FIG. 2b, a greatly enlarged view of a portion of a traybottom 46, having air apertures 48 is shown. The water at an apertureforms a meniscus 110 which bears the load exerted by water pressureP_(w) from the depth d of the water 112 above. The meniscus resistspassage of water through the aperture because of the combined effects ofsurface tension P_(s) in the meniscus and the positive pressure of theair P_(a) (the differential between the air pressure below the apertureand the air pressure above the water head) acting across the stage frombelow. These act to oppose the effects of P_(w). By sizing the aperturebelow a critical limit, e.g., below about 0.100 inch in practicalsystems, the contribution of the surface tension, P_(s) and the airpressure P_(a) prevent the flow of water down through the hole,preserving the meniscus, under conditions of zero air flow through theaperture. By thus limiting the size of the apertures, it becomespossible to selectively limit the amount of air flow used to the minimumrequired to remove the contaminants in water. In this way the air flowrequired may be minimized, in turn minimizing the quantity ofcontaminated air that must be post-treated. Furthermore, the range ofair flows is controllable over a wide range, e.g., of 20 to 1. Inpractical systems, the actual size of the apertures may be selectedbased on, e.g. , the surface tension of the contaminated water, thedepth of the water in the stage and the desired air flow rate.

The trays include baffles 50, 52, 54 which with tray walls 49, 51, 53,55 form a series of compartments, labelled A, B, C, D, to direct thelateral flow of contaminated water about the tray, as illustratedparticularly in FIG. 2a by arrows 57 and limit mixing of the verticalflow of air between corresponding columns labeled A', B', C', D', asindicated particularly in FIG. 2 by arrows 57. Referring first to FIG.2a, the water, typically about 1-2 inches deep in any tray, isintroduced by a transfer duct 56 which directs water from compartment Dfrom a previous tray into compartment A of the next adjacent tray below(arrow 90, FIG. 2). Within each tray, the water flows in a relativelynarrowly confined flow from compartment A, through baffle aperture 58 tocompartment B, next through baffle aperture 60 to compartment C, andfinally through baffle aperture 62 to compartment D, followed by removalof the water laterally through a transfer duct 56 to compartment A ofthe next tray below. As the water follows this circuitous path, stripperair continuously bubbles 61 (FIG. 2) through the small apertures 48 toremove contaminants from the water by air stripping. The lateral flowpath provides a desired duration residence time of water within thestage and enhances stripping efficiency without increasing strippervertical height. Within each stage the contaminated water becomesprogressively less contaminated as it passes progressively throughcompartments A, B, C, and D since the residence time, i.e. degree ofexposure to the stripper air, increases. Similarly, the water in eachtray is successively cleaner than the tray above.

The air flow passes vertically upward through the stages. In any givenstage, the air above the water is progressively less contaminated as afunction of lateral position within the tray, in the same direction thatthe water becomes progressively cleaner flowing laterally through thetray. Referring to FIG. 2, the baffles 50, 52, 54 of each tray arealigned to separate the vertical flow of air into columns A'-D',corresponding to the chambers A-D of the trays. In this arrangement, thebaffles do not interfere or deflect the vertical flow of air and furtherserve to stabilize vertical flow and minimize the mixing of air flowfrom adjacent lateral positions in the tray. It will be appreciated,therefore, that in each column, the flow of air is substantiallyvertical, such that the air from the previous stage contacts the waterin the next stage at the same lateral position. The L-shaped transferduct 56 assures that water is introduced to each successive tray at apoint directly below the introduction point of the previous tray. Thisconfiguration has the particular benefit of enhancing mass transfer ofcontaminant species from the contaminated water to the stripper air byproviding a substantially consistent ratio of contaminationconcentration of the air above the water to the equilibriumcontamination of the water. That is, for example, in the instance ofcolumn D', the relatively cleanest air passes through and is mixed withthe cleanest water in each tray, i.e., the water in tray compartment D.Similarly, the most contaminated air is that passing through column A',since it is this column that is exposed to the most contaminated waterof each stage, that in compartment A.

Referring to FIG. 3, the relative contaminant concentration verses traychamber and vertical stage is illustrated for contaminated water in thestripper. As the plot indicates, the water becomes progressively lesscontaminated as it flows laterally in each tray from chambers A-D and asit passes downward through the stripper from stages 30 to 44, resultingin a concentration gradient laterally and vertically and substantiallycontaminant-free water at chamber D of stage 14. Referring now to FIG.3a, the contamination of water and air is shown as a function of lateralposition within a tray for two adjacent trays, a lower tray and anadjacent higher tray (representative of trays above the bottom-mosttray). As illustrated, both water and air are progressively lesscontaminated, progressing laterally between compartment A to D. Becauseair is mixed with water at the same lateral location of each verticaltray, the difference in relative contaminant concentration between waterand air remains substantially constant, or at least generallyconsistent, from tray to tray for the same lateral position.

Manufacture

Referring now to FIGS. 4-4c and 5-5b, each tray is separated fromadjacent trays by an air permeable tray bottom 46, e.g., of rectangularshape having a length L₁, about 24 inch and width w₁, about 20 inch. Thetray bottom is preferably formed of 20 gauge 304 stainless steel (T₁,about 0.036 inch) or punctured or molded plastic and includes aperturesof d₁, about 0.050 inch spaced S₂, about 1/4 inch on center (FIG. 4a).An exit aperture 74 (3.5 inch by 2.375 inch) is provided at a positioncorresponding to tray compartment D enabling the flow of water treatedin each tray to pass through transfer duct 56 to compartment A of thenext tray.

The transfer duct 56 is constructed of stainless steel or molded plasticand includes an inlet aperture 76 and outlet aperture 78 fortransporting water laterally to the stage below at a point directlybelow the introduction of the previous stage (FIG. 4b). The transferduct 56 includes a one-way check valve, with a valve plate 88, which maytravel in a radial fashion along ring member 89 such that, during starup, the vertical flow of water in the direction of arrow 90 is permittedfor passage of water between adjacent stages but flow of air in oppositedirection to the arrow 90 is prevented. The valve thus prevents largequantities of air from passing through the stripper during system startup when little or no water is present in the tray to provide a waterlock to the normally-submerged outlet of the transfer duct. As evident,the transfer duct prevents the vertical flow of air upward through asmall portion of compartments A and D where introduction and removal ofwater from the trays takes place. The transfer duct 56 is fixed to thetray bottom 46 by means of screws 79 and sealed with a neoprene 1/16inch thick gasket 80. Transfer duct 56 is seated on a ledge 59 cut inthe baffle 52 of the troy.

The baffles 50, 52, 54 and baffle wall piece 81 are positioned in a traybody 82 and secured, e.g., by press fit or ultrasonic welding. The troybody 82 has a width W₂, about 28 inch, and length 1₂, about 32 inch and,as discussed, a height H₅ about 6 inch. The overall area of the stripperstage is thus less than about 900 in². The body 82 includes a ledge 84upon which rests the troy bottom 46.

Referring to FIG. 5, for interlocking adjacent trays, a frame gasket 86(lower frame gasket shown in FIG. 4) is seated in a cut-out 100 of thelower portion of the body and a protuberance 102 on the upper portion ofthe body fits therein to form a sealing engagement when the trays areplaced under compression (e.g., by straps 95, 96, FIG. 1a). A bafflegasket 83 formed of neoprene, seats on the edges of the baffles 50, 52,54 (polyethylene, 1/4 inch thick) (FIG. 4c). The baffle gasket has aU-shaped configuration, with baffles 50, 52, 54 fitting within the U andthe back of the U resting against the tray bottom 46, as illustrated inFIGS. 5-5b. The structure thus permits sealed separation between thevertical columns and structural support for the tray bottoms.

Use

The system is particularly useful for decontamination of watercontaminated with volatile organic compounds (VOC) which may beintroduced to Found water through leakage of a storage tank or the like,as illustrated in FIG. 1. A typical example is a gas station from whichVOCs have leaked into the groundwater. Chemical species that make up thecontamination include gasoline components, e.g., MTBE (methyl tert-butylether) and the BTEX compounds (benzene, toluene, ethyl benzene andxylenes) as well as other water insoluble, high vapor pressurecompounds. It will be understood, that the system may be used otherwise,e.g., for remediation of water contaminated with typical dry cleaningchemicals such as chlorinated hydrocarbons and the like, or othervolatiles such as ammonia or H2S. Typically, even contaminant chemicalswhich are substantially insoluble with water dissolve into the water inrelatively low concentrations (about 1% or less) that neverthelessprevent many uses of the water, e.g., as drinking water. At thecontamination site, the degree and type of contamination ispreliminarily determined by sampling the groundwater from which analysisthe initial configuration and operating conditions of the remediationsystem of the invention can be determined. These conditions include, inparticular, the size and percent open area of the apertures in the traybottoms, which must be selected based on the surface tension of thecontaminated water. The tray bottom in successive trays can be optimizedbased on the variation in surface tension effected by the removal ofcontaminants of the water at successive trays, or for dealing withpotential fouling contaminants. For example, the size of the openingsmay decrease from the top stage toward the bottom stage with the largeropenings near the higher stages receiving the deposits thus effectivelyserving to filter the water for the lower stages. The number of stagesrequired is also determined from the initial analysis. The remediationsystem, easily broken down into stages, is transported to the site andconstructed. By virtue of the modular design and low profile, assemblymay be easily performed by one man without working at great heights. Theair decontamination capacity and mode is also selected based on theinitial analysis. The low physical profile of the apparatus does notgenerally adversely affect the aesthetics of the site. If desired, theapparatus may be housed in a single story building.

During the course of remediation, the progress of the decontaminationand the proper operation of the system may be monitored periodically bya single maintenance worker. The pressure, measured, e.g., at the top ofthe stripper unit, can be read as an indication of fouling of the airpermeable trays. The worker can also easily remove the trays to visuallycheck for fouling and perform cleaning. Replacement of the porousbottoms can be effected at low cost, as needed. The system can be variedto maximize efficiency. For example, variations in contamination levelmay dictate providing fewer or more stages, ,which can be easilyinserted or removed from the stripper tower. Likewise, the tower may beeasily serviced, e.g., tray bottoms may easily be cleaned or replaced inthe case of blockage of the apertures due to sediments or hard waterdeposits. Air flow can be adjusted over a wide range.

Other Embodiments

It will be understood that many variations are possible. For example,where as rectangular trays are illustrated in the embodiments describedherein, other shapes, e.g., circular cross-section trays may beadvantageously employed. Likewise, the tray bottoms can be formed ofvarious material, particularly resistant to specific chemicalcontaminants found on site. For example, the tray bottoms may beconstructed of brass, plastic, etc. Likewise, other components, e.g.,the tray body and sump can be formed of various materials such asstainless steel. Automatic ultrasonic self-cleaning may be incorporated.The low profile of the system enables its construction and use at spillsoccurring in an indoor setting. The stripper unit may be used without avapor de, contamination system by exhausting the airstream directly intothe atmosphere, preferably through an exhaust duct extending tosufficient height so as to expel the airstream at sufficient height toavoid collection of contaminants at low levels. The blower may bearranged at a position upstream of the stripper unit. The apparatus maybe mounted on a trailer or flat bed for ease of transport. The systemmay be configured for remote monitoring. The system may be sized forvarious capacities, e.g., for water flow rates of greater than 20 gpm.Various configurations of aperture sizes in successive stages can beused. For example, the top two trays may include tray bottoms withapertures larger than the stages below, to enhance faltering ofdeposits, or the upper apertures may be smaller, in the upper stagesthan the lower stages in cases where the surface tension of the waterincreases as the water is decontaminated.

FIGS. 6-10 illustrate a particular alternative embodiment of theinvention which will now be described.

The embodiment illustrated in FIGS. 6-10 provides, like the embodimentshown in the preceding figures, a modular, portable system for airstripping contaminants from water, e.g., ground water, at a remediationsite. Referring to FIG. 6, stripping system 200 comprises a plurality ofinterchangeable demountable tray units 202 stackable one on top ofanother in a sealed manner to form a stripping column 203. Lowermosttray unit 202 is sealably secured to sump 204, whereas uppermost trayunit 202 is attached to sealing cap member 206. Mounted directly on sump204 is a vacuum pump assembly 207 comprising a vacuum pump 209 and adiagonally braced L-shaped metal mounting bracket 211. A vacuum pumpenclosure 208 (having an open bottom and side) covers vacuum pump 209and is secured to sump 204 and mounting bracket 211. Vacuum pumpenclosure 208 serves to protect vacuum pump 207 from damage, e.g., fromthe elements and during transportation of system 200, and allows forcooling of the pump as will be described hereinafter.

As in the first embodiment, tray units 202 comprise hollow, lightweightrotationally molded peripheral frames 210 (separately labelled in FIGS.8-10). Likewise, sump 204 and cap member 206 preferably comprise hollowrotationally molded plastic (e.g., polyethylene) pieces. Enclosure 208is preferably formed of rotationally molded plastic as well. Spacedaligned vertical ribs 212 are preferably provided on each rotationallymolded component for added structural rigidity and ease of handling.

Each frame 210 removably retains on its upper periphery a substantiallyhorizontally oriented sheet member 214 formed of plastic or stainlesssteel and provided with a plurality of small apertures (perforatedarea), as in the first embodiment. Frames 210 should have a heightsufficient to separate adjacent sheet members 214 from each other toprevent entrainment of water through the sheet members 214 due to frothformation and hurled water droplets generated in the tray units 202 bythe stripping air during operation. Practice has shown that for waterflow rates of up to 8 gpm, a 7 in. height tray is sufficient. For waterflow rates above 8 gpm and up to 20 gpm, a 10 in. height tray is moresuitable.

Stripping system 200 provides a simplified water flow path as comparedwith the embodiment of FIGS. 1-5. A single baffle plate 216 per traycreates a generally U-shaped lateral flow path across each tray. Baffleplate 216 is secured to sheet member 214 (e.g., by spot welding in thecase that sheet 214 is made of stainless steel) and is fitted within aU-shaped slot 222 provided in frame 210.

Secured to the undersurface of all but the lowermost of sheet member 214(e.g., by screws 220) is a simplified water transfer duct (downcomer)218 (which may be constructed of stainless steel) to transfer water to anext lower tray unit 202. Transfer duct has a completely openrectangular inlet 219 and an outlet in the form of a slot 221 extendingacross a side face of transfer duct 218. The width of outlet slot 221 isadjustable by virtue of plate 223 which is movable vertically andsecurable by screws 223a extending through slots 223b (only one pairlabelled) provided in plate 223. By adjustment of the width of slot 221,a wide range of water flow rates can be accommodated, while minimizingair flow through the transfer ducts 218, especially in a start-upcondition. By placing outlet slot 221 on a side face of the transferduct and providing a bottom surface converging toward slot 221, water istransferred smoothly from an upper to lower tray unit 202. Also securedto sheet member 214 in front of transfer duct inlet 219 (e.g., by screws220) is a weir 225 which determines the quiescent depth of water in trayunits 202, and influences the froth height in tray units 202 inoperation of system 200.

An alternative transfer duct arrangement is illustrated in FIG. 8a. Inthis design, tabs 214a on sheet member 214' engage slots 218a providedin rectangular transfer duct 218' which conveniently may be formed ofmolded or extruded plastic material. A portion of transfer duct 218'extending above the surface of sheet 214' is sized to correspond to thedesired water depth and froth height in trays 202. Thereby, the need fora separate weir structure is avoided. A plastic molded or extrudedconstruction avoids a weld seam of a stainless steel transfer duct whichmay allow stripping air to leak into the transfer ducts, undesirablyallowing the air to bypass the small apertures in sheets 214.

A transfer duct 218" attached to lowermost sheet member 214 (see FIG. 6)may be constructed generally like ducts 218, 218' described above.However, duct 218" should be long enough to extend almost to the bottomof sump 204 so as to remain submerged in water 234 (to avoid air flowtherethrough). Also, the bottom of duct 218" may be left completely opento provide a simple water outlet.

Hollow frames 210 are designed to provide a dual gasket arrangement 211for ensuring a tight seal (1) between adjacent trays 202 assembled oneon top of the other and (2) between each sheet member 214 and itssurrounding frame 210. Around the upper peripheral surface of each tray210 extends a rib-like protuberance 224 which mates with a correspondingouter recess 226 provided in the bottom peripheral surface of each frame210. Gasket material 226a fills recess 226 and becomes compressed byprotuberance 224 when multiple trays are assembled, in order to providea tight sealing engagement of adjacent tray units 202. A second innerrecess 228 is filled with gasket material 228a which abuts against a topperipheral portion of a sheet member 214 resting on an inner peripheralledge 229 of a lower frame 210 when the tray units are assembled, inorder to provide a tight seal between sheet members 214 and frames 210such that air cannot bypass the small aperatures in sheet members 214. Asuitable gasket material is EPDM, an ethylene propylene polymer, whichmay be separately formed with a generally cylindrical cross-section(e.g., 1/2 in. diameter) and cemented in recesses 226, 228.

Whereas in the first illustrated embodiment a strap and tie downarrangement is used to secure the stacked tray units to each other, thesump and the cap member, system 200 utilizes individual fastenersassociated with each tray 202, sump 204 and cap member 206, e.g.,stainless steel latches 230 (see FIG. 7) to fasten these componentstogether. A plurality of fasteners, e.g., ten, are spaced about theperiphery of each frame 210 in order to apply a substantially uniformcompressive pressure about peripheral mating surfaces of the frames 210.Mating latch components are preferably positioned as closely as possibleto the mating surfaces of each frame 210, sump 204 and cap member 206.This minimizes the amount of plastic material put under compressionwhich in turn results in minimized distortion of the stripper componentsand hence increased seal integrity.

Sump 204 provides a base upon which stripping column 203 formed ofstackable tray units 202 and cap member 206 is mounted. As best seen inFIG. 6, a mounting surface 232 for lowermost tray unit 202 is providedon a slightly raised platform of sump 204. Mounting surface 232 has,like the top of each frame 210, a rib-like protuberance 233 for matingengagement with the gasket material in outer gasket recess 226 oflowermost tray unit 202, and a flat ledge surface on which a lowermostsheet member 214 may rest and sealably engage with the gasket materialin inner recess 228.

As in the first illustrated embodiment, sump 204 allows for temporarystorage of decontaminated water 234 passed through stripping column 203.As described in connection with the first embodiment, this water can bedirected to flow from sump 204 back into the ground via piping 22 andrecharge gallery 24 (see FIG. 1 ), or to any other predetermined storagelocation. Preferably, sump 204 is equipped with a sump probe assembly235 for sensing the water level in the sump, whereby operation of a pumpfor removing water from the sump can be controlled and/or the system canbe automatically shut down if a malfunction causes the sump to fill toan unacceptably high level.

Sump 204 is also provided with an air inlet 236 through which air isdrawn into the stripping column 203. In particular, the inlet of vacuumpump 207 communicates via piping 237 with the inside of cap member 206through a mist eliminator 238, similar to mist eliminator 60 in thefirst illustrated embodiment. The vacuum generated by pump 207 draws airthrough inlet 236 into sump 204 and up through the perforated sheets 214of each tray unit 202 in order to perform the stripping action by acountercurrent flow of water and air as water flows laterally across anddownwardly through the stacked tray units 202 in a sequential manner.Air inlet 236 may be provided with a known type of adjustable air flowregular or restrictor 241 for increasing the negative pressure causedwithin stripping column 203 by vacuum pump 207 in order to enhance thevolatization of contaminants in the water.

Enclosure 208 covers air inlet 236 as well as pump 207, and L-shapedbracket 211 is provided with a passageway 239 which allows air to flowinto the enclosure and through inlet 236 during operation of the system.Vacuum pump or blower 207 is cooled by the flow of air thereacrosswithin enclosure 208. Further, this arrangement advantageously mayprovide slight heating of the stripping air which should facilitatewater to air transfer of volatile contaminants. Passageway 239 has aflanged connector to allow for connection of a conduit which may, e.g.,lead to the outdoors in the event system 200 is set up in a climatecontrolled building, whereby building heating or cooling losses due tooperation of the system are avoided. Passageway 239 is also preferablyscreened or filtered to avoid the introduction of foreign matter intothe system. Contaminated air is exhausted from pump 207 through aconduit 243 extending through L-shaped bracket 211 and to an appropriatestack or air decontamination device (e.g., 27 as shown in FIG. 1 )

The water and air flows within stripping column 203 are now described infurther detail. Contaminated water enters the top tray 202 via piping240 extending through cap member 206. The water takes, within the toptray, a U-shaped path across the perforated area of the sheet member 214as illustrated by arrow 242 in FIG. 10a. The water then drops throughtransfer duct (downcomer) 218 directly downwardly onto the sheet member214 of a next lower tray, having a transfer duct 218 mounted on anopposite side of baffle plate 216, as shown in FIG. 10b. In this lowertray the water follows a reverse U-shaped path as shown by arrow 244.The direction of water flow thus alternates between clockwise andcounter-clockwise directions from tray to tray. Practice has shown thatexcellent de, contamination efficiencies can be obtained with thesimplified construction, whereby manufacturing and maintenance costs canbe reduced.

EXAMPLE

A stripping system in accordance with the embodiment of FIGS. 6-10 hasbeen constructed and tested as follows. Each tray unit 202 was providedwith a sheet 214 formed of stainless steel and having regularly spacedcircular apertures with a diameter of 0.047 in. providing an open areaof between 4 and 5% of a total sheet area of 480 in² (sheets 214measured 24 in.×20 in., with the tray frames 210 measuring overall, 23in. in width, 27 in. in length and either 7 or 10 inches in height).Transfer ducts 218 extended above sheets 214 to create a weir height(equal to quiescent water depth on trays) of 1 in. The open top of eachtransfer duct measured 3.0 in.×7.75 in. and a 5/8' in. widthwise slotwas provided at the bottom of each transfer duct. So constructed, with astripping column 203 comprising 6 trays, a water flow rate from severalto 10 gpm, and an air flow rate in the range of 100 to 175 CFM,decontamination levels of between 99.90 and 99.99% were obtained forfeed water contaminated with the four BTEX compounds. Comparabledecontamination levels are obtainable for water flow rates of up to 20gpm with airflow rates up to 250 CFM. Furthermore, it is believed thatMTBE is removable from water with similar efficiencies. Finally, higherefficiencies are generally obtainable by adding additional tray units202 to stripping column 203.

It can thus be seen that very high de, contamination levels areobtainable with a relatively low air flow rate (thereby reducing thesignificant costs involved in subsequently treating the stripper air)and with an unobtrusive, easy to transport, assemble and service, lowprofile apparatus. (The overall height of a 6 tray system is 5.5 feetfor 7 in. high trays and 7 feet for 10 in. high trays, sump 204 and capmember 206 each measuring 1 ft. in height.)

The invention has been illustrated and described in terms of preferredembodiments thereof. Other embodiments within the scope and spirit ofthis invention will occur to those having ordinary skill in the art uponreading this disclosure.

We claim:
 1. A method of treating contaminated water, comprising thesteps of:pumping contaminated water to an elevated position; directingthe water to flow laterally across and downwardly through a series ofsubstantially horizontal trays sealed to each other to form a strippingapparatus; flowing air upwardly through said stripping apparatus, whilesaid water flows downwardly from tray to tray through downcomers andlaterally across a perforated area of said trays, in such a manner thatthe air passes through a plurality of apertures of the perforated areahaving a diameter no greater than 0.100 inch and through the water as itflows laterally across each tray, whereby contaminants in the water aretransferred to the air flowing upwardly, with substantially no waterseepage through said apertures; exhausting air from the strippingapparatus for subsequent treatment; and recovering decontaminated waterwhich has passed through the stripping apparatus.
 2. A method accordingto claim 1, wherein the water being decontaminated in groundwater pumpedfrom the group for decontamination and returned to the ground followingdecontamination.
 3. A method according to claim 1, wherein the aperturesthrough which the air is passed have a diameter of less than 0.050 inch.4. A method according to claim 1, wherein the apertures through whichthe air is passed provide an open area of each tray of less than 20%. 5.A method according to claim 1, wherein the apertures through which theair is passed provide an open area of each tray of 2% to 9%.
 6. A methodaccording to claim 5, wherein the aperatures through which the air ispassed provide an open area of each tray of 4% to 5%.
 7. A methodaccording to claim 1, wherein the air is pumped through the strippingapparatus at a flow rate no greater than 250 cubic feet per minute andwater is passed through the stripping apparatus at up to 20 gallons perminute.
 8. A method according to claim 7, wherein the water is passedlaterally across and downwardly through a series of no more than eighttrays to obtain a decontamination level of at least 99.99%.
 9. A methodaccording to claim 7, wherein the water is passed laterally across anddownwardly through a series of no more than six trays to obtain adecontamination level of at least 99.90%.
 10. A method according toclaim 1, wherein the contaminants being removed from the water comprisevolatile organic compounds.
 11. A method according to claim 10, whereinthe contaminants being removed from the water comprise BTEX compounds.12. A method according to claim 10, wherein the contaminants beingremoved from the water comprise MTBE.
 13. A method according to claim 1,wherein the air is drawn through the stripping apparatus by a vacuumpump which creates a negative pressure within the stripping apparatus.14. A method according to claim 1, wherein the water is directed to flowacross said trays in a substantially U-shaped path, alternatelyclockwise and counterclockwise from tray to tray.
 15. A method oftreating contaminated water, comprising the steps of:pumpingcontaminated water to an elevated position; directing the water to flowlaterally across and downwardly through a series of individuallydemountable substantially horizontal tray units sealed to each other toform a stripping apparatus; drawing air upwardly through said strippingapparatus using a vacuum pump which creates a negative pressure withinthe stripping apparatus, while said water flows downwardly from trayunit to tray unit through downcomers and laterally across a perforatedarea of said tray units, in such a manner that the air passes through aplurality of apertures of the perforated area, whereby contaminants inthe water are transferred to the air flowing upwardly; exhausting airfrom the stripping apparatus; and recovering decontaminated water whichhas passed through the stripping apparatus.
 16. A method according toclaim 15, wherein the water being decontaminated is groundwater pumpedfrom the ground for decontamination and returned to the ground followingdecontamination.
 17. A water air stripper system usable to treatcontaminated water, said water air stripper system being usable with ablower arranged to cause air flow upwardly through a stripper unit ascontaminated water flows downwardly through the stripper unit, saidwater air stripper system comprising:a vertical assembly of a series ofindividually demountable tray units, on which the contaminated waterflows, mounted above one another to form said stripper unit, a bottom ofeach tray unit comprising an air-porous medium defined by a sheet memberhaving air-flow apertures, each tray unit being constructed to retainwater for a period of time during stripping action caused by air passingupwardly through the apertures, and including an internal baffle thatdefines a tortuous water flow path laterally across each tray unit, saidbaffles extending respectively between, and substantially sealed to, theundersurface of an adjacent upper tray bottom and an upper surface ofthe tray bottom in which the baffle resides; water entry means and exitmeans respectively at top and bottom ends of said water air stripperunit, and water-flow guiding means to guide said water at a relativelyshallow depth over the air-porous medium of each tray unit, thencedownwards to a next tray unit; and air inlet and outlet conduitsrespectively at the bottom and top ends of said stripper unit.
 18. Thewater air stripper system of claim 17 wherein said assembly comprises avertically-extending interfitting nest of demountable tray frames, eachair-porous medium comprising a porous bottom member which is removablyheld in each frame.
 19. The system of claim 18 wherein said water-flowguiding means comprises a transfer duct arranged to guide the leastcontaminated groundwater of a said tray unit to flow downwards to aposition in an adjacent lower tray unit such that the water entering theadjacent lower tray unit will contact the most contaminated air passingthrough said adjacent lower tray unit.
 20. The system of claim 19 inwhich substantially all said tray units are provided with a saidtransfer duct.
 21. The system of claim 17 wherein patterns of thebaffles of the series of tray units are positioned substantiallyidentically above one another to form a vertically arranged series ofbaffles and the water is guided from tray unit to unit such that thewater proceeds progressively in repeated fashion through identicalpatterns of airstreams as it progressively releases its contaminantsduring its course of lateral travel through each of the each of theseries of units.
 22. The system of claim 21 wherein said verticallyarranged series of baffles provides adjacent vertical columns for theflow of stripper air, said columns being arranged to maintain,throughout the series of tray units, at any lateral position in thewater flow path, a substantially consistent ratio of contaminationconcentration of the air and the water through which the air passes. 23.The system of claim 17, further comprising a volatilized contaminantremoval device connected to receive contaminated air from the stripperunit, and an air blower arranged to cause air flow upwardly through thestripper unit, said volatilized contaminant removal device constructedand arranged to remove volatilized contaminants stripped from said waterand carried by said air as said air moves through said stripping unit.24. The system of claim 23 wherein said volatilized contaminant removaldevice comprises a preheater and an oxidation unit.
 25. The system ofclaim 23 wherein said volatilized contaminant removal unit comprises atleast one of an absorbent and adsorbent.
 26. The system of claim 17wherein said system is constructed to decontaminate water at a flow rateof about 20 gpm.
 27. The system of claim 17 wherein said system isconstructed for an air flow rate of about 250 CFM or less.
 28. Thesystem of claim 17 wherein air is drawn into said stripper unit from ablower or vacuum pump, the intake of which is connected to the top endof said stripper unit.
 29. The system of claim 17 further comprisingadjustment means for varying an air flow volume through the stripperunit over a range of about 20 to
 1. 30. The system of claim 17 whereinsaid air porous medium is removable and disposable.
 31. The system ofclaim 17 wherein said air-porous medium has openings of about 0.050 inchdiameter.
 32. The system of claim 17 wherein said air porous medium is athin, flexible sheet having a thickness of 0.06 inch or less.
 33. Thesystem of claim 17 wherein said assembly of tray units is arranged suchthat the size of said air-flow apertures decreases in successive trayunits from the top end of the stripper unit.
 34. The system of claim 17wherein said stripper tray units have an area of less than about 1,000in².
 35. The system of claim 17 wherein said tray units have peripheralframes formed of rotationally molded plastic.
 36. The system of claim17, wherein said stripper unit further comprises a sump for receivingwater passed through said series of tray units.
 37. The system accordingto claim 36, wherein said sump is formed of rotationally molded plastic.38. The system of claim 17 wherein said stripper tray units have avertical height of about six inches.
 39. The system of claim 38 whereinsaid stripper unit has a vertical height of about nine feet or less. 40.The system of claim 17 wherein said water air stripper unit comprises atleast five of said tray units.
 41. The system of claim 40 wherein saidair stripper unit comprises six to ten of said tray units.
 42. The waterair stripper system of claim 17, wherein said apertures have a diameterof about 0.100 inch or less to prevent the flow of water therethrough atsubstantially zero air flow through the apertures under conditions ofequality between a head of water in the tray above the apertures and anopposing pressure differential of the air below and above the tray. 43.A water air stripper unit usable to treat contaminated water at aremediation site, said stripper unit comprising a vertically-extendinginterfitting nest of demountable tray frames, each tray frame having aporous bottom member which is removable from the frame and an internalbaffle that defines a tortuous water flow path laterally across thebottom member of each tray, said baffle extending respectively betweenand substantially sealed to, an undersurface of the next above traybottom member and the upper surface of the tray bottom member in whichthe baffle resides.
 44. A liquid remediation apparatus for strippingcontaminants from a liquid via air flow, comprising:a plurality ofindividually demountable tray units stacked vertically one on top ofanother to form a stripping unit, each tray unit comprising a sheetmember having air-flow apertures, and a baffle that defines a tortuouswater flow path across each said tray unit in a lateral direction;liquid entry and exit means provided at upper and lower ends of saidstripping unit, respectively, for providing a liquid flow through saidstripping unit; and air entry and exit means provided at said lower andupper ends, respectively, for providing an air flow through the liquidflowing in said stripping unit; wherein the baffles of respectivestacked tray units are configured one above another such that aplurality of substantially isolated vertical air-flow columns are formedin the stripping unit, whereby air passing from one tray to another traycontacts liquid in said another tray at the same lateral position, andmass transfer of contaminant species from the liquid to the air isenhanced due to a substantially consistent ratio of contaminationconcentration of the air and the liquid through which the air passes,from tray to tray, within a respective one of said air-flow columns. 45.An apparatus according to claim 44, wherein each tray unit comprises aframe formed of molded plastic material from which said sheet member isremovable.
 46. An apparatus according to claim 45, further comprising aplastic molded base to which said stripping unit is secured, said baseproviding air passageways into said vertical air-flow columns and a sumpfor storage of liquid passed through the stripping unit.
 47. Anapparatus according to claim 46, wherein said stacked tray units aresecured to said base member by a strap and tie down ratchet arrangement.48. An apparatus according to claim 44, wherein said tray units areshaped so as to securely nest with each other when stacked.
 49. Anapparatus according to claim 44, wherein said apertures are sized so asto prevent the flow of water therethrough at substantially zero air flowthrough the apertures under conditions of equality between a head ofwater in the tray above the apertures and the opposing pressuredifferential of the air below and above the tray.
 50. An apparatusaccording to claim 44, wherein each said baffle extends respectivelybetween, and is substantially sealed to, an under surface of an adjacentupper tray sheet member and an upper surface of the tray sheet member inwhich the baffle reside.
 51. A liquid remediation apparatus forstripping contaminants from a liquid via air flow, comprising:aplurality of individually demountable tray units stacked vertically oneon top of another to form a stripping unit, each tray unit comprising asheet member for supporting liquid which flows across said member andhaving air-flow apertures to allow air to flow upwardly through thestripping unit and through the liquid which flows across each tray unit,and a frame formed of molded plastic material shaped so that said trayunits securely nest with each other when stacked to form a fluid tightseal during operation of said apparatus; and a plastic molded basemember to which said stripping unit is secured, said base memberproviding air passageways into said stripping unit, and a sump forstorage of liquid passed through the stripping unit, said stacked trayunits being secured to said base member by a strap and tie down ratchetarrangement.
 52. A water air stripper system usable to treatcontaminated water, said water air stripper system being usable with ablower arranged to cause air flow upwardly through a stripper unit ascontaminated water flows downwardly through the stripper unit, saidwater air stripper system comprising:a vertical assembly of a series ofindividually remountable tray units, on which the contaminated waterflows, mounted above one another to form said stripper unit, a bottom ofeach tray unit comprising an air-porous medium defined by a sheet memberhaving air-flow apertures, each tray unit being constructed to retainwater for a period of time during stripping action caused by air passingupwardly through the aperatures; water entry means and exit meansrespectively at top and bottom ends of said water air stripper unit, andwater-flow guiding means to guide said water at a relatively shallowdepth over the air-porous medium of each tray unit, thence downwards toa next tray unit, said water-flow guiding means comprising a transferduct arranged to guide the least contaminated groundwater of a said trayunit to flow downwards to a position in an adjacent lower tray unit suchthat the water entering the adjacent lower tray unit will contact themost contaminated air passing through said adjacent lower tray unit,said transfer duct including a check valve to prevent air flowtherethrough during a start-up condition.
 53. A water air strippersystem usable to treat contaminated water, said water air strippersystem being usable with a blower arranged to cause air flow upwardlythrough a stripper unit as contaminated water flows downwardly throughthe stripper unit, said water air stripper system comprising:a verticalassembly of a series of individually demountable tray units, on whichthe contaminated water flows, mounted above one another to form saidstripper unit; a bottom of each tray unit comprising an air-porousmedium defined by a sheet having air-flow apertures, each tray beingconstructed to retain water for a period of time during stripping actioncaused by air passing upwardly through the apertures; water entry meansand exit means respectively at top and bottom ends of said water airstripper unit, and water-flow guiding means to guide said water at arelatively shallow depth over the air-porous medium of each tray unit,thence downwards to a next tray unit; and air inlet and outlet conduitsrespectively at the bottom and top ends of said stripper unit; wherein,said water-flow guiding means comprises a transfer duct arranged toguide the least contaminated groundwater of a said tray unit to flowdownwards to a position in an adjacent lower tray unit such that thewater entering the adjacent lower tray unit will contact the mostcontaminated air passing through said adjacent lower tray unit, andbaffle means are sealed to top and bottom surfaces of successive traybottoms in a manner to isolate airstreams passing through regions ofwater in a tray unit that have different levels of contaminants.
 54. Awater air stripper system usable to treat contaminated water, said waterair stripper system being usable with a blower arranged to cause airflow upwardly through a stripper unit as contaminated water flowsdownwardly through the stripper unit, said water air stripper systemcomprising:a vertical assembly of a series of individually demountabletray units, on which the contaminated water flows, mounted above oneanother to form said stripper unit, a bottom of each tray unitcomprising an air-porous medium defined by a sheet member havingair-flow apertures, said apertures having a diameter of about 0.100 inchor less to prevent the flow of water therethrough at substantially zeroairflow through the apertures under conditions of equality between thehead of water in the tray above the apertures and the opposing pressuredifferential of the air below and above the respective tray, saidair-porous medium having an open area of about 2 to 9% of a surface areathereof, each tray being constructed to retain water for a period oftime during stripping action caused by air passing upwardly through theapertures; water entry means and exit means respectively at top andbottom ends of said water air stripper unit, and water-flow guidingmeans to guide said water at a relatively shallow depth over theair-porous medium of each tray unit, thence downwards to a next trayunit; and air inlet and outlet conduits respectively at the bottom andtop ends of said stripper unit.
 55. The system of claim 54 wherein saidair-porous medium has an open area of about 4 or 5% of a surface areathereof.
 56. A water air stripper unit usable to treat contaminatedwater at a remediation site, said stripper unit comprising:a verticalassembly of a series of individually demountable tray units, each trayunit having a porous bottom member for allowing air to pass therethroughand water to pass thereover, and an internal baffle that defines atortuous water flow path laterally across the bottom member; and atransfer duct arranged to guide water from one of said tray units to anext lower tray unit; wherein:a plurality of zones of differing aircontamination concentrations are set up laterally across each tray unitwhen water is passed downwardly through the stripper unit and air ispassed upwardly through said water; and water being transferred fromsaid one tray unit to said next lower tray unit enters initially a zoneof said plurality of zones in said next lower tray unit, having amaximum air contamination concentration, and thereafter flowssequentially into remaining zones of said plurality of zones in an orderof decreasing air contamination concentration.
 57. A portable modularstripping system usable to treat contaminated water on site,comprising:a plurality of individually demountable and interchangeabletray units stackable one on top of another to form a stripping column,each tray unit comprising a hollow plastic molded tray frame, a sheetmember having air-flow apertures, a baffle defining a lateral water flowpath across each sheet member, a transfer duct arranged to guide waterthrough the sheet member after having traversed said lateral water flowpath, and sealing means for creating an air and water tight seal betweenadjacent tray frames when said tray units are stacked to form saidstripping column; water entry and exit means provided at upper and lowerends of said stripping column, respectively, for providing water flowthrough said stripping column; and air entry and exit means provided atsaid lower and upper ends, respectively, for providing an air flowthrough the liquid flowing in said stripping column.
 58. A systemaccording to claim 57, wherein said water exit means comprises a hollowplastic molded sump to which a lowermost tray unit is sealablysecurable, for temporarily storing decontaminated water passed throughthe stripping column.
 59. A system according to claim 58, wherein saidsump is formed of rotationally molded plastic.
 60. A system according toclaim 58, wherein said stripping column further comprises a hollowrotationally molded cap member secured to an uppermost one of said trayunits.
 61. A system according to claim 58 wherein said sump includes anair inlet through which air is drawn to flow through the strippingcolumn.
 62. A system according to claim 61 further comprising a vacuumpump for drawing air through the stripping column and creating anegative pressure therein, and wherein said air inlet has air-flowrestricting means for increasing said negative pressure.
 63. A systemaccording to claim 58, further comprising a vacuum pump mounted on saidsump for drawing air through the stripping column.
 64. A systemaccording to claim 63, further comprising enclosure means mounted onsaid sump for enclosing said vacuum pump and coveting an air inlet insaid sump for drawing air from within said enclosure means through saidstripping column, said enclosure means having a first passageway forallowing air to enter said enclosure means and a second passageway forexhausting air from said vacuum pump, whereby the air drawn into thestripping column initially passes over and cools the vacuum pump withinthe enclosure means.
 65. A system according to claim 57, wherein saidtray frames are formed of rotationally molded plastic.
 66. A systemaccording to claim 57, further comprising a vacuum pump for drawing airthrough the stripping column and creating a negative pressure therein.67. A system according to claim 66, wherein said air entry meanscomprises air flow restriction means for increasing the negativepressure created in the stripping column by the vacuum pump.
 68. Asystem according to claim 57, wherein each said tray unit furthercomprises fastener means for sealably securing adjacent tray unitstogether, one on top of another.
 69. A system according to claim 68,wherein said fastener means comprises a plurality of stainless steellatches.
 70. A liquid remediation apparatus for stripping contaminantsfrom a liquid via air flow, comprising:a plurality of individuallydemountable tray units stackable vertically one on top of another toform a stripping column, each tray unit comprising a sheet member havingair-flow apetures, and a baffle defining a lateral water flow pathacross the sheet member of each said tray unit; a sump to which alowermost tray unit may be sealably secured, for temporarily storingdecontaminated water passed through the stripping column; a vacuum pumpmounted on said sump for drawing air through the stripping column; andenclosure means mounted on said sump for enclosing said vacuum pump, andcoveting an air inlet in said sump for drawing air from within saidenclosure means through said stripping column, said enclosure meanshaving a first passageway for allowing air to enter said enclosure meansand a second passageway for exhausting air from said vacuum pump,whereby the air drawn into the stripping column initially passes overand cools the vacuum pump within the enclosure means.
 71. A portablemodular stripping system usable to treat contaminated water on site,comprising:a plurality of individually demountable and interchangeabletray units stackable one on top of another to form a stripping column,each tray unit comprising a tray frame, a sheet member having air-flowapertures, a baffle defining a lateral water flow path across each sheetmember, a transtar duct arranged to guide water through the sheet memberafter having traversed said lateral water flow path, and sealing meansfor creating an air and water tight seal between adjacent tray frameswhen said tray units are stacked to form said stripping column; waterentry and exit means provided at upper and lower ends of said strippingcolumn, respectively, for providing water flow through said strippingcolumn; and air entry and exit means provided at said lower and upperends, and a vacuum pump in fluid communication with said air exit means,for drawing air through the liquid flowing in said stripping column. 72.A system according to claim 71, wherein said air entry means comprisesadjustable air flow restriction means for varying a negative pressurecreated in the stripping column by the vacuum pump.